Abstract Affinity reagents are essential to almost any modern scientific investigation of human disease. Antibodies are the most widely used family of affinity reagents and when cloned and produced in culture represent a powerful tool that can be continually regenerated. Many monoclonal antibodies boast strong interactions, slow off-rates, and good specificity. To supplement monoclonal antibodies, the Baker laboratory at the University of Washington has developed techniques to design small proteins de novo that bind molecules of interest. The overall goal of this Core entitled, ?Affinity Regent Characterization Core,? is to provide the reagents needed for Projects 2 and 3 by (1) developing new monoclonal antibodies to be used in different assays, (2) labeling antibodies and novel small protein affinity reagents for use in CyTOF and brain imaging, and (3) carefully characterizing each reagent to ensure that different batches of affinity reagents behave similarly.